§ 2034.310.Experts not designated on party's list; testimony at trial; permissible conditions

Section 2034.300's exclusion rule would be too rigid without an escape valve for a couple of situations where fairness runs the other way, and this section supplies it. A party may call as a witness at trial an expert that party never designated if either of two conditions is met. The first covers an expert someone else designated: if that expert has since been deposed under Article 3, the party who did not designate the expert can still call the expert at trial, since the opposing side already had full notice of the expert and a chance to question the expert directly.

The second condition covers pure impeachment. An undesignated expert can take the stand solely to impeach the testimony of an expert offered by another party at trial. That impeachment can attack the factual foundation underneath the opposing expert's opinion, testimony that a fact the opposing expert relied on is false or does not exist at all. What it cannot do is cross the line into contradicting the opinion itself; an undesignated expert brought in for impeachment stays confined to undercutting the foundation, not offering a competing conclusion.